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Episodic Tremor and Slip (ETS) Event Monitor

Episodic Tremor and Slip (ETS) events in southern Vancouver Island happen every 14 to 16 months. The ETS phenomenon is marked by subtle surface displacements, accumulating over a period of days to weeks, that are opposite in direction to the longer-term deformation trends. These displacement transients are accompanied by distinct seismic tremors that have the appearance of background noise but are recorded at multiple stations.

This page displays the time series of daily position changes at continuous GPS sites, selected from the WCDA and PBO networks. Positions are estimated from the Bernese 5.0 program using rapid precise orbits (IGR) produced by the International GNSS Service ( IGS ). The changes are with respect to the GPS site at Penticton (DRAO) which is assumed fixed on the North America Plate and the displayed time-series have been zero-meaned. Day-to- day variations in position common to ALL network sites are most likely due to changes at the reference site. During the winter season, we also expect snow accumulation on antennas to cause spurious changes in position up to several centimetres (e.g. WSLR). The graphs are updated daily as soon as the analysis results become available.

The arrangement of the time series in the display below corresponds roughly to the sites' relative geographic locations. ELIZ is located on the west coast of northern Vancouver Island, P423 is at the southeast extreme of the sub-array being displayed. For a clearer indication of site locations, please see the GPS sites map. Choose a component (Latitude, Longitude, or Height) and submit this choice to see updated graphs of all sites. Clicking on individual site graphs will display all three components for that site in a single pane.

NOTE: The data are analyzed using IGR orbits with one day delay, and the analysis results are normally updated at 20:00 UT daily.

The GPS sites map shows the location of the sites used in this monitor tool.